Apparatus for treating plastics material

ABSTRACT

A device for treating plastics material, in particular thermoplastic plastics material, has a receiving container ( 1 ) which has a base ( 15 ) and lateral walls ( 14 ). In the receiving container at least [one] disc ( 17 ) is arranged close to the base ( 15 ), and is driven by a vertical shaft ( 18 ) so as to rotate about its axis and carries tools ( 22 ), as a result of which a circulating movement about the axis of the shaft ( 18 ) is imparted to the material present in the receiving container ( 1 ). At least one blade ( 26 ) which projects beyond the edge of the disc ( 17 ) in the direction towards the lateral wall ( 14 ) is fastened to the said edge of the disc ( 17 ) adjacent to the lateral wall ( 14 ). The blade is inclined with respect to the horizontal plane in such a way that the plastics material moved by the tool ( 22 ) or the tool carrier ( 16 ) during its circulation is given an upwardly directed movement component.

The invention relates to a device for treating plastics material, inparticular thermoplastic plastics material, having a receivingcontainer, which has a base and lateral walls, and having tools, whichare arranged in the receiving container and which are carried by a shaftwhich passes through the base of the receiving container in a sealedmanner and which is driven by a motor so as to rotate about its axis, atleast one tool being fastened on a tool carrier, designed in the form ofa disc, on the top face of the disc, the disc being situated close tothe base of the receiving container so that the plastics materialpresent in the receiving container is set in a circulating movementabout the axis of the shaft.

Devices of this type are known (e.g. AT 375 867 B, AT 407 970 B or WO93/18902). On account of the rotating tool carriers or tools, theplastics material being treated is flung by the action of centrifugalforce against the lateral wall of the container. A portion of thisplastics material rises along the lateral wall of the container andcirculates in the form of a mixing cone, but eventually drops back intothe centre of the container again. This results in the desired dwellperiod of the treated particles of plastics material in the receivingcontainer, so that the plastics material introduced into it isthoroughly mixed, is sufficiently heated by the frictional forces whichoccur, and, in the case of tools which have a comminuting effect uponthe plastics material, is also sufficiently comminuted. It has beenfound, however, that the plastics material flung towards the lateralwall of the container does not all rise up on the said wall, but aportion goes down below the lowest tool or below the lowest disc forminga tool carrier. There this portion of plastics material can become fusedon in an uncontrolled manner as a result of friction. Attempts have beenmade to avoid this drawback by the attachment of conveying ribs on theunderside of the said disc, but this step is not entirely satisfactory.

The object of the invention is to avoid with little outlay the drawbackdescribed, so as thereby not only to reduce the susceptibility of thedevice to breakdown, but also to treat in a more uniform manner all theplastics material introduced into the receiving container, since theresidue of plastics material in the region of the container base, i.e.below the lowest tool, is effectively counteracted. This object isattained according to the invention in that the disc carries, inaddition to the tools, at least one blade which projects beyond the edgeof the disc in the direction towards the lateral wall of the receivingcontainer and is inclined with respect to the horizontal plane in such away that the plastics material flung off from the disc by the tools isgiven an upwardly directed movement component during its circulation.Irrespectively of whether the circulation of the plastics material isnow carried out only by the tools or, in addition, by tool carrierscarrying the latter (individual tools or tool carriers could be formedby rods alone which project outwards from the shaft in the horizontaldirection), the moved plastics material is deflected upwards by way ofthe blades, and this effectively prevents the material from droppingdown. This effect can be utilized not only to prevent, to the greatestpossible extent, the treated plastics material from dropping below thelowest tool carrier formed by the disc, but also in order that plasticsmaterial which has dropped down may be immediately returned to therevolving mixing cone again and is not fused on below the lowest toolcarrier with friction during a prolonged dwell period in an uncontrolledmanner. If a plurality of tool carriers are arranged one above the otherin a plurality of planes, then the blades in the upper tool carriersresult in a displacement of the circulating plastics material upwardsand thus in a prolongation of the dwell period.

In accordance with a preferred embodiment of the invention, the bladealso projects upwards and below beyond the disc, in order to make aslarge as possible the active area acting upon the plastics material.

Since, as already mentioned, discs arranged in the base region of thereceiving container and forming [the] tool carriers are known, withinthe scope of the invention it is possible for already existing plants ofthis type to be re-fitted without difficulty.

Further characterizing features and advantages of the invention may beseen in the description of embodiments which are illustrateddiagrammatically in the drawing.

FIG. 1 is a vertical section through a device according to theinvention;

FIG. 2 shows a disc-shaped tool carrier designed with blades, in anaxonometric view;

FIG. 3 is a view in the direction of the arrow III in FIG. 2;

FIG. 4 is a plan view in the direction of the arrow IV in FIG. 2;

FIG. 5 is a section along the line V-V in FIG. 1, and

FIG. 6 shows a detail of FIG. 5 in a side view.

The device as shown in FIG. 1 has a receiving container 1 with acircular cross-section and with a vertical axis 2, into which theplastics material to be treated, in particular of a thermoplasticnature, for example PETP (polyethyleneterephthalate), is introduced inthe form of grinding material consisting bottles or bottle pre-forms,sheets, flakes etc. from above through a charge opening 3. If thematerial to be treated has to be treated under vacuum, the said opening3 has a sluice 4 attached to it, the sluice chamber 5 of which can beclosed off by two slides 6, 7 which can be moved in a reciprocatingmanner by double-acting cylinders 8, 9. A filling funnel 10, into whichthe material to be treated is introduced batch-wise or continuously by asupply device (not shown), for example a conveyor belt, is attached tothe sluice 4 at the top. An evacuation line 11, which leads to anevacuation device 12, is attached to the sluice chamber 5. A furtherevacuation line 13 leads from the receiving container 1 to theevacuation device 12.

The receiving container 1 has vertical lateral walls 14 and a horizontalbase 15. A tool carrier 16, which is formed by a horizontal circulardisc 17 (see FIG. 2 also), is arranged close to the base 15, thecircular disc 17 being mounted on a shaft 18 which passes through thebase 15 in a vacuum-tight manner and which is driven by a motor 19 so asto rotate in the direction of the arrow 20. The top face 21 of the disc17 of the tool carrier 16 carries a plurality of tools 22 which aredistributed at uniform intervals about the periphery of the tool carrier16 and which act upon the plastics material present in the container 1during the rotation of the disc 17. As a result, the said plasticsmaterial is caused to circulate about the axis 2, and, on the otherhand, centrifugal force seeks to move the plastics material in theradial direction towards the lateral wall 14. A mixing cone 23 is formedin such a way that a portion of the plastics material rises along thelateral wall 14, reaches a culmination point 24 during this circulationand finally drops back again into the region of the container axis 2.Not all the plastics material takes part in this ascent, however, sincea portion of the plastics material flung off from the disc 17 seeks toenter the space 25 below the disc 17. In order to prevent this, the disc17 carries a plurality of blades 26 (see FIGS. 2 to 4 also) which arearranged distributed at uniform intervals about the periphery of thedisc and each of which can be formed by a flat plate 27, the plane ofwhich is directed radially with respect to the centre of the disc 17,but is arranged at an inclination to the vertical direction. This angleof inclination a (FIG. 3) can be selected differently depending upon thefield of application in question, advantageous angles of inclinationbeing between 15 and 30° according to experience. This arrangement andinclination of the blades 26 relative to the plane of the disc 17 of thetool carrier 16 has the effect that during the rotation of the disc 17in the direction of the arrow 20 a theoretical force vector 28 (FIG. 2)is exerted upon the particles of plastics material moved by the blade 26in each case (ignoring other, relatively insignificant influencingvariables, such as friction of the particles against one another etc.).When projected into a vertical plane, this force vector 28 has acomponent 29 (FIG. 3), and when projected into a horizontal plane (FIG.4) it has a horizontal component 30. The vertical component 29 is formedfrom two portions 31, 32. The portion 31 extends from the point 33 underconsideration in each case in a direction which is orientatedtangentially to a circle—passing through the point 33—about thecontainer axis 2 which coincides with the axis of the shaft 18. Thisportion is produced by the shear force acting in the rotating directionof the disc 17. The portion 32 extends from the point 33 underconsideration in each case in a vertical direction and is produced bythe inclination of the plate 27 of the blades 27. This verticalcomponent 29 is at a right angle to the plane of the plate 27.

In the horizontal projection (FIG. 4) the horizontal component 30 has aportion 34, starting from the point 33 in the above-mentioned tangentialdirection, and a portion 35, which is produced by centrifugal force andwhich extends in the radial direction of the disc 17.

The said blades 26 impart a preferred movement upwards to the plasticsmaterial flung off from the disc 17 by the tools 22 and thus effectivelyprevent portions of plastics material from being able to enter the space25 below the disc 17 of the tool carrier 16 during the treatment of thematerial in the container 1. This can be assisted by ribs 37 which arearranged on the bottom face 36 of the disc 17 and which are arranged insuch a way, radially for example, that the plastics material present inthe space 25 is conveyed in the direction towards the lateral wall 14.The plastics material moved outwards in this way is then engaged by theblades 26 and is conveyed upwards again.

An increase in the energy introduced into the plastics material presentin the container 1 during the rotation of the tool carrier 16 can beachieved in that guide faces in the form of guide blades 38 (FIG. 1) areattached to the inside of the lateral wall 14 of the receiving container1, the guide blades 38 preventing, when arranged appropriately, theparticles of plastics material circulating in the container 1 from beingable to escape freely upwards and thus absorbing relatively littleenergy in the form of frictional heat. Expressed in simple terms, theparticles of plastics material ascending upwards encounter the guideblades 38 in the direction of the arrow 39 and, as a result, receive amovement component in the horizontal direction (arrow 40). Thisdeflexion of the moved particle of plastics material has the effect thatpart of its kinetic energy is converted into frictional energy and, as aresult, the particle is heated.

In order to be able to adapt to different conditions, it is advantageousfor at least one of the guide blades 38 to be made adjustable. Thiscould be carried out by changing the active area of the guide blades 38,for example by insertion into the container to different degrees. Whatis structurally more advantageous is an adjustment of the angle ofinclination of the guide blades 38 by means of a shaft 41 (FIGS. 1, 5)which is connected to it and which passes through the lateral wall 14 ofthe container 1 and is mounted in a bearing 42 fastened to the lateralwall 14. The said shaft 41 can be rotatable manually, for example bymeans of a hand wheel, or by a motor. A motor-driven adjustment device50 is illustrated in FIGS. 5 and 6. The shaft 41 is connected to a pivotlever 43 to which the piston rod 44 of a double-acting cylinder 45 isarticulated, the end of which remote from the pivot lever 43 is mountedin a non-displaceable, but pivotable manner. The piston 46 guided in thecylinder 45 is acted upon with pressure medium by a pressure-mediumshaft 48 by way of lines 47, the said pressure-medium shaft 48 beingcontrolled in any suitable manner, preferably electronically, in amanner dependent upon the nature of the plastics material to be treated.

As a rule, it is advisable to monitor the temperature of the plasticsmaterial present in the receiving container 1, in order to keep itsheating to the desired level or to control it in a suitable manner. Tothis end it is possible for at least one temperature probe 49 to beprovided in the receiving container 1, the temperature probe 49 beingadvantageously arranged on the inner face of the lateral wall 14 and ina vertical region in which the mixing cone 23 is present. One or more ofthe said temperature probes 49 can be used to control the adjustmentdevice 50 for at least one of the guide blades 38, and this is indicatedby a line 51 in FIG. 5. In addition or alternatively to this, thetemperature probe or probes 49 can be connected by way of a line 52(FIG. 1) to a regulating device 53 which controls the rotational speedof the motor 19 by way of a line 54.

As shown in the drawing, each blade 26 projects in the radial directionbeyond the periphery of the disc 17 of the tool carrier 16. In addition,the blade also extends upwards and downwards beyond the top face 21 orthe bottom face 36 of the disc 17, in order to increase the active areaof each blade 26. The plate 27 of each blade 26 can be provided with aslot 55 in which the edge of the disc 17 engages. It is also possible,however, for the arrangement to be reversed, i.e. an arrangement withthe slot in the disc 17, in which case the non-slotted plate 27 thenengages in the said slot. This connexion can be secured by welding or insome other suitable manner. In many cases, however, it will be advisablefor the plate 27 to be fastening to the disc 17 by screwing.

The plate 27 of each blade 26 need not be flat, and it would be possiblefor the plate 27 to be curved slightly, the concave side being arrangedon the leading side of the plate. Such a curvature could have the effectthat the particles of plastics material slide for a brief time on theplate 27 before they are deflected upwards. This would result in agentle acceleration and treatment of the particles of plastics material.

It may be seen in FIG. 2 that the blades 26 are arranged offset withrespect to the tools 22 in the peripheral direction of the disc 17. Itis more favourable, however, for the blades 26 to be arranged in acontinuation of the tools 22, which is illustrated in FIG. 1 and has theadvantage that the particles of plastics material moved by the tools 22in the direction of the arrow 56 (FIG. 1) are guided directly onto theblades 26.

The above-mentioned arrangements of the blades 26 can also be made indesigns in which a plurality of tool carriers 16 are arranged one abovethe other, in which case it is not necessary for all the tool carriersto be constructed in the form of discs and to be provided with blades,but only the tool carrier 16 situated closest to the base 15 of thecontainer.

It would also be possible for the blades 26 to be provided, not on thedisc-shaped tool carrier 16, but directly on the tools 22.

As a rule, the plastics material to be treated is introduced alreadycomminuted beforehand into the receiving container 1. If comminution inthe container 1 is necessary, the tools 22 can be formed accordingly,for example as cutters with cutting edges 57 (FIG. 2).

1. Apparatus for treating plastics material, comprising a receivingcontainer, which has a base and lateral walls as well as at its top acharge opening for the material to be treated, tools arranged in thereceiving container and carried by a shaft which passes through the baseof the receiving container in a sealed manner, said shaft being drivenby a motor so as to rotate about its axis, at least one tool beingfastened on a tool carrier designed in the form of a disc on the topface of the disc, which disc being situated close to the base of thereceiving container so that the plastics material present in thereceiving container is set in a circulating movement about the axis ofthe shaft, wherein the disc carries, in addition to the tools, aplurality of blades which project beyond the edge of the disc in thedirection towards the lateral wall of the receiving container, theactive surface of the blades being inclined with respect to thehorizontal plane in such a way that the plastics material flung off fromthe disc by the tools is given an upwardly directed movement componentduring its circulating, and wherein the blades also project upwards andbelow beyond the disc.
 2. Apparatus according to claim 1, wherein eachblade is formed by a plate which is fastened on the disc obliquely tothe plane of the said disc.
 3. Apparatus according to claim 2, whereineach blade is formed by a flat plate.
 4. Apparatus according to claim 1,wherein the edge of the disc carries a plurality of blades which aredistributed at equal intervals about the periphery of the disc. 5.Apparatus according to claim 4, wherein the blades are offset relativeto the tools in the peripheral direction of the disc.
 6. Apparatusaccording to claim 1, wherein, as viewed in the radial direction of thedisc, at least one blade adjoins the tool on the outside or is arrangedin a continuation of the tool.
 7. Apparatus according to claim 1,wherein ribs, which convey plastics material present below the discoutwards in the direction towards the blades, are provided on the bottomface of the disc.
 8. Apparatus according to claim 1, wherein at leastone blade has a slot into which the edge of the disc is inserted, or thedisc has a slot into which the blade engages, or the blade is fastenedto the disc by screwing.
 9. Apparatus according to claim 1, wherein theblades are inclined by 15 to 30° relative to the vertical plane. 10.Apparatus according to claim 1, wherein at least one blade is madeconcave on its leading side.